1. Field of the Invention
The present invention relates to an AC generator for vehicles loaded on cars, trucks and the like.
2. Description of the Related Art
Recently, the engine and the whole electric appliances come close to the road surface due to the slant nosing for reducing the vehicle running resistance and improving the visibility, and the water-splashing conditions caused by splashing water from tires during the running have been severe. Further, in the cold district, a large amount of salts such as calcium chloride and sodium chloride are scattered for the purpose of preventing the road from freezing in a winter season, and the salts stay on the road surface as electrolytic solutions, which are dragged in during the running, resulting in harsher corrosive environment of the engine. Since the vehicular generator loaded on the engine is exposed to the harsh environment as described above, an inconvenience of corrosion caused by water-splashing and salts sometimes occurs.
On the other hand, with the tendency of a narrower engine room, there is no room for a loading space for the vehicular generator. Further, the reduction in weight for improving fuel cost and the enhancement of generation performance resulting from an increase in such as electric load of safety control apparatus and so on have been demanded. Needless to say, lower cost is demanded.
That is, an AC generator for vehicles which is excellent in resistance to corrosion, small in size, light in weight, and low in cost has been necessary. In this case, the stoppage of the generation of the electrical energy due to the corrosion is mainly caused by the fact that in the step of mounting of a stator coil into a slot of a stator core, an insulating film on the surface of the stator coil is damaged by mechanical friction or the like, and when particularly salt water which is an electrolytic solution is splashed on the damaged portion, it reacts with copper that is an electric conductor of the coil to produce a conductive compound. When this reaction progresses, separation between the film and the copper is further accelerated, a short-circuit between the stator core and the coil and between the coils occurs, resulting in an occurrence of lowering of output and local rapid heat generation, finally leading to a breakage of the stator coil.
For solving the problem, it is contemplated that the film of the stator coil be increased in thickness, and the damage resistance be improved. Further, in the impregnation process by way of resin generally carried out for the resistance to vibration and the environmental effect after the stator coil has been wound, thickly coating of impregnated resin is generally used. Further, as disclosed in Japanese Patent Application Laid-Open No. Hei 3-235644, a drip proof cover is mounted on the cooling air take-in side to cut off a path entering water directly from the outside.
When the film of the stator coil is increased in thickness, not only the material cost of the film increases but also the number of coating of the film increases. Therefore, the number of fabrication steps of the coil material increases so that the cost of the stator coil considerably increases. Further, since the occupied area ratio in the slot increases by the portion in which the film becomes thick, an occurrence of damage of the film when the stator coil is inserted and mounted increases, failing to improve the anti-corrosion performance as desired. Further, if the film is increased in thickness to provide the same space factor, a sectional area of copper becomes narrow so that the electric resistance value of the stator coil rises, thus lowering the output. There are also problems of a rise in temperature resulting from deterioration of heat radiation of the stator coil itself, and the lowering of output therefrom. When the area of the slot is enlarged so as to provide the same space factor in order to compensate for the lowering of output, the physique cannot but increase in order to secure a magnetic path section in each part of the stator core in terms of the magnetic circuit, which cannot attain the demand for miniaturization.
It is needless to say that when the film excellent in resistance to damage is provided, the cost rises. However, the generator which is high in cost ratio of the stator coil occupied by the entire constituent product is greatly affected by the rise of cost as compared with other constituent products. If the film is increased in thickness, when the heat resistance to the film is improved with respect to the rise of temperature, the cost further increases.
Also in the case where the impregnated resin is coated thickly, needless to say, there poses problems of an increase in material cost, an increase in production cost due to the increase of the steps, and the lowering of output due to the rise of temperature.
Further, in the method disclosed in Japanese Patent Application Laid-Open No. Hei 3-235644, in a recent small and high-output vehicular generator, a fan is provided on the side of a rotor, by which rotation cooling air is taken therein, and a stator coil is cooled by utilizing air discharged through a window provided diametrically of a frame, as described in the embodiment shown in FIG. 11 thereof. That is, since the stator coil is positioned near the window for ventilation provided diametrically of the frame, water or salt water from the diametrical outside of the generator can easily reach the periphery of the stator. Therefore, it is contemplated that a drip-proof cover is also mounted externally of the window provided diametrically of the frame, or a window covered by water out of the windows provided diametrically of the frame is blocked as shown in FIGS. 4A and 4B. In any case, however, the ventilation resistance increases and the quantity of cooling air reduces, and an escape of hot air after heat generating parts such as a stator coil, a rectifier is impeded, resulting in rising considerably a temperature of the whole generator. Further, the addition of the drip proof cover increases materials and production cost due to an increase in number of parts.
The present invention solves the above-described problem of prior art. An object of the present invention is to provide an AC generator for vehicles which prevents corrosion caused by water-splashing from outside to achieve a long service life, is excellent in cost, is free from a new problem such as a rise of temperature, and can realize miniaturization and reduced weight.